This invention relates generally to X-ray tube monitoring systems and is concerned more particularly with apparatus for safely measuring the current in a high voltage anode circuit of an X-ray tube.
In the operation of a conventional X-ray tube, the cathode and anode target electrodes generally are maintained at suitable electrical potentials, such as a negative and a positive seventy-five kilovolts relative to ground, respectively, for example, to establish a strong electrostatic field therebetween. As a result, electrons emitted from the cathode are beamed electrostatically onto the anode target with sufficient energy to generate X-rays. Thus, the beamed electrons impinging on the anode target represent an anode current which flows from an external high voltage source through a connecting circuit to the anode target of the X-ray tube.
In order to measure the anode current, a current measuring means, such as a meter, for example, generally is connected in the anode circuit between the high voltage source and the X-ray tube. However, this places the current measuring meter at the high voltage level of the anode target. Consequently, the current measuring meter usually is enclosed within a shockproof housing in order to ensure the safety of personnel operating the equipment. Thus, the current measurements are not available for remote viewing by conventional low voltage means, such as an oscilloscope or a digital meter, for examples.
Furthermore, the current measuring meter generally is of the movable coil type having a response time which provides an average of the anode current over the measurement time interval. However, if the anode current waveform were displayed on an oscilloscope, instantaneous variations in the anode current could be seen. Also, the anode current waveform may disclose X-ray tube defects, cable leakage, stray capacitance, and the like.
Therefore, it is advantageous and desirable to provide X-ray tube monitoring apparatus with means for safely transmitting measurements of anode current from the high voltage levels of the anode circuit to an isolated readout device at relatively low voltage levels.